Spaced helically wound cable



, .-No v. 7,- 1967 c. GNERRE T 3,351,706

SPACED HELICALLY WOUND CABLE Filed March 18, 7 196 5 Z-Sheets-Sheet 1 vINVENTORS.

C. Gerald Gnerre Ralph DiNunzio v. BY Cm,Wn -42 amt! ATTORNEYS UnitedStates Patent-O 3,351,706 SPACED HELICALLY WOUND CABLE C. GeraldGrierre, Belmont, and Ralph Diuunzio, Lexington, Mass, assignors toSimplex Wire and Cable Company, Cambridge, Mass., a corporation ofMassachusetts Filed Mar. 18, 1965, Ser. No. 450,231 1 16 Claims. (Cl.174-105) I This invention relates to a method for applying spacedhelical wire servings to oblong objects, such as electrical conductors.

It is often desirable to provide wire servings about oblong objects,such as tubes and electrical conductors, for the purpose of addingstrength and armor protection to the finished product and in some casesfor the purpose of providing an additional conductor to the overallcomposite. Moreover, it is often economical to apply such servings inspaced relationship to each other in instances where partial coverage issatisfactory.

Helical wire servings have, however, been generally avoided where lessthan about 90% surface coverage is used becauseof the difiiculty inapplying the individual wire strands in uniformly spaced relationship toeach other and alsobe'cause of the difficulty in holding such spacedwire in place during subsequent handling and use.

It is, therefore, an object of this invention to provide a method forapplying spaced helical wire to oblong objects, such as electricalconductors and tubes, and for holding such wire in place duringsubsequent handling and use. These and other objects are accomplished byhelically applying wire strands in equally spaced relationship to eachother about a ribbed core. Preforming the wire is frequently desirableto reduce its tendency to change position on the core and to facilitateapplication of the wire strands in uniformly spaced relationship withrespect to each other. Preforming also reduces the tendency of thewrapping to pop out of place when the conductor is put under stress andincreases the flexibility of the product.

The ribs on the 'core, which are incorporated in the core at itsformation oraddedin the form of, a tape,

that of the wire to be applied over them. The size of the can bestraight or they can be helical with a lay opposite ribs will vary withthe diameter of he wires to be used and the hardness .of the core.Generally the radial height of the ribs ranges from one-third totwo-thirds ofthe diame ter of the overlying helical wire. The presenceof the ribs on the core greatly aids in maintaining the spacing of theoverlying wire during application of the wires and during subsequenthandling and processing, and increases the permissable angle of lay ofthe wire, therefore, providing further economies.

A particularly advantageous application of this invention is in themanufacture of small armored submarine cable for deep water service. Insuch instances using polyolefin insulation it is often possible torealize a good cable modulus with less armor wire than would be requiredto cover the entire surface of the cable. By the method of thisinvention such conductors can b provided with spaced helical armorwires, covering 50% or less of the conductor core, which wire provides ahigh strength, light weight cover having sufiicient external protectionin the circumstances and greater flexibility than has been heretoforerealized in such cable. Further, such cables can be made with greaterease and uniformity than has heretofore been supposed possible.

In the usual case the ribs are incorporated with the core during theextrusion of the polyolefin insulation and can be formed easily by usingslotted extrusion dies. The size and shape of the ribs are controlled bythe size of the slots, which in turn is afunction of the extrusiontechnique used, and the material characteristics of the extrudate. Theshape of the outer surface of each rib can be of semi-circularcross-section, pointed, flat or of any other desired configuration, and,as stated above, the radial height of each rib generally ranges fromone-third -to two-thirds the diameter of wire used. The number of ribsused varies depending on the relative diameters of the core andoverlying wire and on the severity of service anticipated.'Generallybetween 2 and 5 ribs are sufficient, although a greater or lesser numbercan be used," but in the usual case the number willv not be so largethat the overlying wire is supported solely by the ribs without touchingthe core between adjacent ribs. It is anticipated that the overlyingwire will be applied about theribs and core under sufficient tension tocause depression of the ribs, locking the ribs and wire securelytogether. For this reason the width of the ribs should be quite small,each one to three degrees of the circumference covering about of thecore. a

As suggested above, the overlying wire, particularly when it is toserveas mechanical protection for the overlying core, is preferablypreformed. Preformed armor Wire has been previously used, for example,in well logging cables. In that application armor wire is applied in alayer covering generally 94to of the external surface of the cable.Preforming of the overlying wire is preferably carried out in the samemanufacturing line in which the wire is applied to the cable core bypassing each strand, as it is served about the core, over a set ofrollers which are spaced and oifset to give the desired pitch diameterand lay. In this manner each strand of wire is permanently shaped into apredetermined helix which hugs the core and has no tendency to pop outof position when the cable is under stress. Tension applied to preformedarmored cable is thus evenly distributed among the individual wirestrands.

After application of the'overlying wire to the cable, an external layerof plastic or rubbery material can be applied to hold the wire even morefirmly in place against dislodging forces which may be encounteredduring subsequent use. Alternatively the cable can be drawn through areducing die in which the overlying wire is pressed deeply into the ribsand, if desired, into the core to make a form-fitting depression whichlocks and holds the'wire preventing subsequent wire displacement andeliminating the need of any form of external binding. It will beunderstood, however, that the choice of such post application Cable 1Cable 2 A ngle ofLay. deg l7 5 Breaking Strength, p.s.i 4, 500 4, 600Percent Elongation a Break N 0. turns under 500?! Load l9 1 2 1 Per 200ft.

As noted above the application of overlying wire about a ribbed coreenables the use of longer lay than has heretofore been deemed possiblewithout noticeable displacement of the wire during use. For a furtherdescription of the present invention reference is made to the attacheddrawings in which:

FIGURE 1 is a perspective view of a submarine coaxial cable constructedaccording to this invention with each layer broken away successively toshow the details of the cable construction;

FIGURE 2 is a section taken along lines 22 in FIGURE 1;

FIGURE 3 is a perspective view of an underground residential powerdistribution cable constructed according to the present invention, witheach layer broken away successively to show the details of the cableconstruction;

FIGURE 4 is a section taken along lines 44 in FIG- URE 3;

FIGURE 5 is a schematic plan view of an arrangement suitable forapplying spaced helical wire to cables and tubes according to thepresent invention;

FIGURE 6 is a sectional view taken along line 6-6 in FIGURE 5;

FIGURE 7 is a sectional view taken along line 7-7 in FIGURE 5; and

FIGURE 8 is a sectional view taken along line 88 in FIGURE 5.

Referring more particularly to FIGURE 1 a submarine coaxial cable 29 isshown consisting of a central metallic conductor 30 embedded in a layer32 of dielectric material and with a braided conductor 34 of wirestrands located between an inner layer 32 of solid dielectric and anouter layer 36 of solid dielectric. Outer layer 36 includes fourintegral, longitudinal ribs 38 spaced at equal arcuate intervals aboutits exterior. A layer 39 of twelve, equally spaced, preformed helicalarmor wire strands 40 partially covers dielectric layer 36 and is inturn encased in an external insulating jacket 42 with strands 40actually embedded in jacket 42. Both central conductor 30 and braidedconductor 34 are copper or other highly conductive material anddielectric layers 32 and 36 are preferably of a polyolefinic material,such as polyethylene. Jacket 42 can, for example, be made of apolyolefinic material or of rubber. Armor wire strands 40 normally aresteel.

As will be noted especially with reference to FIG- URE 2, each rib 38extends radially from jacket 36 a distance equal to slightly more thanone-half the diameter of each armor wire strand 40 and is relativelynarrow, covering only two or three degrees of the circumference ofdielectric layer 36. As noted above each strand 40 of armor wire ispreformed immediately prior to its application about dielectric layer 36and is applied under sufficient tension to make depressions in ribs 38at all points of intersection of armor wire strands 40 and ribs 38. Eachstrand 40 is in contact with outer dielectric layer 36 in the spacebetween adjacent ribs 38. V Referring to FIGURE 3 an undergroundresidential power distribution cable is shown having a central conductor12. A thick layer 14 of solid dielectric is extruded about conductor 12,while a relatively thin, exteriorly ribbed layer 16 of semi-conductingmaterial is extruded about dielectric layer 14, and a layer 17 of spaceddrain wire 18 is served helically about layer 16. Layers 14 and 16 canbe polyethylene or other extrudable substance.

As will be seen from FIGURE 4 semi-conducting layer 16 includes threelongitudinal ribs 20, equally spaced about layer 16. Ribs 20 extendradially outward from the general cylindrical contour of layer 16, adistance equal to about one-half the diameter of drain wires 18, theirwidth covering no more than two or three degrees of the circumference oflayer 16.

In the cable shown in FIGURE 3, layer 17 of drain wires 18 is intendedto act as a conductor and preferably tin-coated copper is used. Eachdrain wire 18 is applied under sufficient tension to cause a depressionof ribs 20 and cable 10 is then pulled through a reducing die to deepenthese depressions and also to cause some depression to be made in thesurface of layer 16 between ribs 20 by drain wires 18.

In FIGURE 5 a schematic representation of a manufacturing arrangementsuitable for practicing the method of the present invention is shownconsisting of an extruder 50, a stranding machine 52 and a post-windingstation 54. At extruder a layer 56 of polyolefin insulation is extrudedabout a central conductor 57 as it passes through a slotted die 59 whichproduces longitudinal ribs 62 on insulation 56. Alternately, extruder 50can be replaced by a taping machine in which longitudinally ribbedinsulating tape is applied to a core with a straight or helical lay ofthe ribs opposite the lay of the wire to be applied over it.

Conductor 57 having insulating layer 56 applied to it then passes tostranding machine 52 in which wire servings 60 are helically applied.Where wire servings 60 are of a relatively hard material such as steel,stranding ma chine 52 preferably includes a preforming head 58 in whicheach wire strand is passed over a set of rollers which are spaced andoffset to give the desired pitch di ameter and lay to the wire prior toits application to the ribbed core. The wire servings 60 are applied toribbed insulation 56 under sufficient tension to cause indentation ofribs 62 at points of intersection of wire 60 and ribs 62. Each strand ofwire 60 is also in contact with layer 56 between adjacent pairs of ribs62. As will be seen from FIGURE 7 wire 60 is evenly distributed aboutthe circumference of ribbed insulation 56.

Post-winding station 54 which is not necessary in all cases, can be areducing die wherein wires 60 are more firmly pressed into ribs 62, or,as illustrated, it can include an extruder for applying an externaljacket 64 of a polymeric or rubbery substance over wire 60 whereby wires60 are even more firmly held in place and protected from theenvironment.

Although the examples illustrated in the drawings are of insulatedconductors and cables, the practice of this invention, it will bereadily apparent, extends to the formation of wire reinforced tubeswhich can serve as conduits. It will thus be noted that manymodifications and variations of the examples are within the scope of theinvention resulting in products which vary from conductors with exposedexternal wire to reinforced tubes with encapsulated wire. It will alsobe noted from the description of the conductor shown in FIGURES 3 and 4that, in instances when the wire servings are made of soft materialsuch'as copper, the wire can be applied directly to the ribbedinsulation while preforming is preferred when steel wire is used.

We claim:

1. The method for applying wire servings in spaced relationship to eachother about oblong objects which includes forming a core having aplurality of radially extending ribs disposed longitudinally thereon atintervals about its circumference, and helically applying a plurality ofwire strands about said ribbed overlying said ribs, in spacedrelationship to each other, said wire strands having been permanentlyshaped into a predetermined helix prior to application about said ribbedcore.

2. The method according to claim 1 wherein said helical wire strands areapplied under sufficient tension to cause indentation of said ribs.

3. The method according to claim 1 wherein said wire strands contactsaid core between adjacent pairs of ribs.

4. The method according to claim 3 wherein said core includes betweentwo and five said ribs, said ribs having a height above said core equalto one-third to two-thirds the diameter of said wires.

5. The method of applying wire servings in spaced relationship to eachother about an electrical conductor which includes forming a layer of asolid dielectric about said conductor, said layer having a plurality oflongitudinal ribs extending radially outward therefrom, said ribs beingdisposed about the external surface of said layer of solid dielectric,and applying a plurality of wire strands in spaced relationship to eachother helically about said layer of solid overlying said ribs undersuiticient tension to cause indentation of said ribs at points ofintersection of said ribs and said wire strands, said wire strandshaving been permanently shaped into a predetermined helix prior toapplication about said layer of solid dielectric.

6. The method according to.claim which further includes applying anexternal coating about said Wire servlngs.

7. The method according to claim 5 which further includes drawing saidconductor with said wire servings thereon through a reducing die.

8. A cable which includes a central electrical conductor, a layer ofsolid dielectric surrounding said conductor, said layer of soliddielectric having longitudinal ribs extending outward therefrom, andspaced wire servings permanently shaped into a predetermined helix andhelically applied about said layer of solid dielectric overlying saidribs.

9. The cable according to claim 8 which further includes an externalcovering surrounding said wire servrugs.

10. The cable according to claim 8 wherein said wire servings arepartially impressed into said layer of solid dielectric.

11. A coaxial cable which includes a central metallic conductor, a firstlayer of solid dieletcric surrounding said central metallic conductor,an outer metallic conductor surounding said first layer of soliddielectric, a second layer of solid dielectric surrounding said outermetallic conductor, said second layer of solid dielectric havinglongitudinal ribs extending outward therefrom, and spaced wire servingspermanently shaped into a pre- 7 layer of solid dielectric overlyingsaid ribs.

12. The cable according to claim 11 which further includes an externalcovering surrounding said wire servings.

13. An underground residential power distribution cable which includes acore consisting of a central metallic conductor and a layer of soliddielectric surrounding said central metallic conductor, longitudinalribs extending outward from said core and spaced Wire servingspermanently shaped into a predetermined helix and helically appliedabout said core overlying said ribs.

14. The cable according to claim 13 wherein said core further includes asecond layer of material surrounding said layer of solid dielectricwhich second layer includes said longitudinal ribs.

15. The cable according to claim 14 wherein said second layer ofmaterial is semiconductive.

16. The cable according to claim 13 wherein said wire servings areelectrically conductive and are partially impressed into said corReferences Cited UNITED STATES PATENTS 3,106,815 10/1963 Nance et al.3,180,926 4/1965 Trill 174 107 3,259,684 7/1966 Wakefield 174 X FOREIGNPATENTS 506,948 6/1939 Great Britain.

LARAMIE E. ASKIN, Primary Examiner. H. HUBERFELD, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,351,706 November 7, 1967 C. Gerald Gnerre et al.

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 1, line 44, for "he" read H the column 4, line 55, after "ribbed"insert core column 5, line 1, after "solid" insert dielectric Signed andsealed this 7th day of January 1969.

(SEAL) Attest:

EDWARD J. BRENNER Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer

8. A CABLE WHICH INCLUDES A CENTRAL ELECTRICAL CONDUCTOR, A LAYER OFSOLID DIELECTRIC SURROUNDING SAID CONDUCTOR, SAID LAYER OF SOLIDDIELECTRIC HAVING LONGITUDINAL RIBS EXTENDING OUTWARD THEREFROM, ANDSPACED WIRE SERVINGS PERMANENTLY SHAPED INTO A PREDETERMINED HELIX ANDHELICALLY APPLIED ABOUT SAID LAYER OF SOLID DIELECTRIC OVERLYING SAIDRIBS.